The present invention relates to an electrophotographic type image forming apparatus such as a copier, printer, and facsimile device, by which a toner image formed on an image forming body by a toner image forming means, is transferred onto a transfer material, fixed and an image is obtained, and in more detail, to an image forming apparatus by which toner images are formed on double sides of the transfer material through an intermediate transfer body, and color double sided images are obtained.
In the conventional double sided image forming apparatus, a method in which the one side image formed on the image forming body is transferred onto the transfer material, fixed and the transfer material is accommodated once in a double sided reversal feeding apparatus, and next, the transfer material is in timed relationship with another side image formed on the image forming body, and is fed from the double sided reversal feeding apparatus, and the image is transferred onto the other side of the transfer material and fixed, is adopted.
In this double sided image forming apparatus, because the conveyance of the transfer material is conducted such that, after the transfer material is accommodated once in the double sided reversal feeding apparatus, the transfer material is fed again, there is a problem that the conveyance distance of the transfer material becomes long, and it takes a long processing time for the double sided image formation. Further, because the transfer material which passes a fixing means once and is easily curled, is fed again, the reliability of the transfer material conveyance is low, thereby, it becomes a cause by which the jamming or wrinkle of the transfer material is caused.
In contrast to this, in Japanese Tokkosho Nos. 49-37538, 54-28740, Japanese Tokkaihei No. 1-44457, or Japanese Tokkaihei No. 4-214576, an image forming apparatus by which the toner images formed by the image forming body are transferred onto the double sides of the transfer material by using an intermediate transfer body, and the double sided image is obtained by one time fixing, and an image forming method are proposed.
Specifically, in Japanese Tokkaihei No. 1-44457, and Japanese Tokkaihei No 4-214576, a method, in which a plurality of the image forming means composed of the image forming body, charging means, imagewise exposure means, and cleaning means, are positioned in parallel on the intermediate transfer body in the order of yellow (Y), magenta (M), cyan (C) and black K), and the double sided copy of the color image is formed, is proposed.
In an image forming apparatus by which a color toner image is formed on the image forming body, and color toner images are formed on double sides of the transfer material through an intermediate transfer body, a plurality of developing devices in which each color toner of Y, M, C and K are accommodated, are provided, and all of developing devices in which each color toner of Y, M, C and K are accommodated, are operated, and toner images of the multi-colored color image are superimposed and formed on the image forming body, and transferred onto the transfer material, or onto the transfer material through the intermediate transfer body. On the one hand, in the case of the image formation of the mono-color, for example, one color of black, only the developing device in which black (K) toner is accommodated, is operated, and one color toner image of black is formed on the image carrier, and transferred onto the transfer material, or onto the transfer material through the intermediate transfer body.
The rear side image formed on the image forming body is transferred onto the intermediate transfer body (primary transfer A). Next, the front side image formed on the image forming body is transferred onto the front side of the transfer material conveyed in timed relationship with the intermediate transfer body (primary transfer B). Further, when the transfer bias voltage is applied onto the transfer material on the front side of which the front side image is held, from above, the rear side image on the intermediate transfer body is transferred onto the rear side of the transfer material (secondary transfer). In this manner, the transfer material on double sides of which the toner images are held, is adhered onto the intermediate transfer body and conveyed, and the separation bias voltage for separation discharging is applied thereon and the transfer material is separated from the intermediate transfer body, and conveyed to the fixing apparatus. In the fixing apparatus, the bias voltage is applied between fixing members (fixing rollers) for nipping and fixing, and fixing without toner disturbance is conducted.
In the image formation, when the image reading or image transmission are carried out, a miss often occurs in the initial period of these operations. For example, reading error caused by jam of document occurs. In the image formation, in the case where the feeding of the transfer sheet is conducted at the same time as the start of the image reading, or as the start of the image transmission, when the miss occurs, the operation is stopped, and the conveyance of the transfer sheet is stopped during the sheet feeding, and in this case, it is necessary that the transfer sheet stopped during the sheet feeding, is taken out as a jammed sheet from the conveyance path of the transfer sheet before the next operation. For clearing the jammed sheet from the conveyance path, a long period of time is necessary for clearing, and further, there is a case in which the surface of the photoreceptor which is the image forming body, is damaged, and the actuator of the sensor provided on the conveyance path is damaged. Furthermore, a lot of transfer sheets are wasted uselessly.
On the one hand, when the sheet feeding is started after the image reading is finished, or after the image transmission is finished, the printing time period from the time of the start of the image reading to the time in which the image is formed on the transfer sheet and the transfer sheet is delivered, becomes long, and the image processing performance is not satisfactory.
In the case of the conventionally known double sided image forming apparatus shown by the conceptual view in FIG. 13, in which the single side (front side) image is formed on the transfer material and is fixed, and after that, the transfer material is fed to the transfer area though the reversal sheet feeding path, and the rear side image is transferred onto the opposite side of the transfer material, and is fixed and the transfer material is delivered, it would be considered to start the feeding of the transfer material after finishing all reading procedure of the initial double sided image.
FIGS. 11(a)-11(c) and FIGS. 12(a)-12(c) are illustrations showing the operation sequence in which, after the reading of the image data of the initial group, and transmission are completed, the feeding of the transfer material is started, in the double sided image forming apparatus shown in FIG. 13. FIGS. 11(a)-11(c) are case where the apparatus has a capacity (length) enough to move the transfer material with an interval which is equivalent to two sheets of A-3 sized transfer material in the reversal sheet feeding path, and the double sided images of the A-3 size are formed, and two sheets are one group, and after the reading (FIG. 11(a)) of the document image of the (1-front), (1-rear), (2-front), and (2-rear) and transfer are completed, the (1-front) image is read from the image storing section (FIG. 11(b)), and the image formation is conducted, and synchronously with that, the feeding of the first sheet (FIG. 11(c)) is conducted. Further, FIGS. 12(a)-12(c) are case where the apparatus has a capacity (length) enough to move the transfer material with an interval which is equivalent to three sheets of A-4 sized transfer material in the reversal sheet feeding path, and the double sided images of the A-4 size are formed, and three sheets are one group, and after the reading (FIG. 12(a)) of the document image of the (1-front), (1-rear), (2-front), (2-rear), (3-front), (3-rear), and transmission are completed, the (1-front) image is read from the image storing section (FIG. 12(b)), and the image formation is conducted, and synchronously with that, the feeding of the first sheet (FIG. 12(c)) is conducted.
As described above, when the sheet feeding is started after the completion of the reading of the document image of one group, even when there is a miss of the initial image reading, because the sheet feeding is not conducted, thereby, the sheet feeding jam is not caused. However, as clearly be seen from FIGS. 11(a)-11(c), and FIGS. 12(a)-12(c), in the double sided image forming apparatus which does not have the intermediate transfer body, but has the reversal path shown in FIG. 13, the time period in which the image is formed on double sides of the first sheet of the transfer material, and the transfer material is delivered onto the delivery tray, is very longer.
On the other hand, because this system needs synchronization between writing image and feeding the transfer material, if the transfer materials are fed with writing procedure before finishing reading procedure for initial document, the system cannot avoid risk that transfer materials are jammed with reaction for reading miss.
In an image forming apparatus by which toner images are formed on double sides of a transfer material through an intermediate transfer body, an object of the present invention is to provide an image forming apparatus in which the processing time required for the printing is not long, and even when a miss which is easily generated at an initial period of the image reading or the image transmission occurs, jam clearing is not necessary at each time.
The above object can be attained by any one of the following structures (1) to (4).
(1) An image forming apparatus in which toner images formed on an image forming body are formed on double sides of a transfer material, the image forming apparatus comprising: reading means for reading image data of original documents; writing means for writing an image on the image forming body according to the image data; feeding means for feeding the transfer material; and an intermediate transfer body, wherein the writing means writes the image for the intermediate transfer body before the feeding means starts to feed the transfer material.
(2) An image forming apparatus, in which toner images formed on an image forming body are formed on double sides of a transfer material, the image forming apparatus comprising: reading means for reading image data of original documents; writing means for writing an image on the image forming body according to the image data; feeding means for feeding the transfer material; and an intermediate transfer body, wherein when the images of n pages can be accommodated on the intermediate transfer body, the feeding means starts to feed the transfer material after the reading means finishes to read the image data of 2n pages, and the writing means starts to write the image data before the reading means finishes to read the image data of 2n pages.
(3) An image forming apparatus in which toner images formed on an image forming body are formed on double sides of a transfer material, the image forming apparatus comprising: reading means for reading image data of original documents; writing means for writing an image on the image forming body according to the image data; feeding means for feeding the transfer material; and an intermediate transfer body, wherein the transmission means transmits the image data in synchronization with a writing by the writing means according to the image data, and the feeding means starts to feed the transfer material after the writing means finishes to write the image data through the intermediate transfer body.
(4) An image forming apparatus in which toner images formed on an image forming body are formed on double sides of a transfer material, the image forming apparatus comprising: reading means.for reading image data of original documents; writing means for writing an image on the image forming body according to the image data; feeding means for feeding the transfer material; and an intermediate transfer body, wherein the transmission means transmits the image data not in synchronization with a writing by the writing means according to the image data, and the feeding means starts to feed the transfer material after the writing means finishes to write the image data through the intermediate transfer body.